Project Summary Receptor-ligand interactions on cells mediate cell-cell and cell-environment communications in many biological processes. Adhesion frequency assay has unique capability of measuring the receptor-ligand interactions at the single-cell level. The measurement can provide important information on the quality of biological processes and for the selection of potent therapeutic cells. Current adhesion frequency assay uses micropipettes to aspirate cells for both interaction measurement and cell transfer afterwards. As a result, it is bulky, labor-intensive, manual- operative, and low-throughput. In order to maximize the potential of adhesion frequency assay in biomedical research and clinical applications, it is necessary to develop high-throughput miniature device. In view of the tremendous potential and challenges in developing high-throughput miniature adhesion frequency assay, I propose a transformative technical route ? on-chip multiplexed adhesion frequency assay ? that will seek to synergize optical manipulation and microfluidics. I will bring in new ideas from different areas, including optical manipulation, optical imaging, microfluidics, cellular biology, and device physics for development, validation and applications of the proposed assay. Specifically, I will (1) address multiplexed-measurement and cell-sorting challenges in the implementation of the assay, (2) characterize, validate and optimize the pre- packaged assay, and (3) assemble and package the assay into a compact device and apply it to screen cells for disease therapy. With the unprecedented capabilities of measuring the receptor- ligand interactions and sorting cells, the proposed assay will change current paradigm of cell profiling and incorporate one of the most important parameters for quantifying cell functions into routine assays. Once fully developed, the on-chip multiplexed adhesion frequency assay will fill many unmet needs in both biomedical research and clinical applications of the receptor-ligand interactions on cells.